Options Greeks: What you should know
The Greeks
Delta – An option’s delta is the rate of change of the price of the option with respect to its underlying security’s price. The delta of an option ranges in value from 0.0 – 1.00 for calls (0 to -1.00 for puts) and reflects the increase or decrease in the price of the option in response to a 1-point movement of the underlying asset price.
Used to measure the change in value of a contract from a $1 change. Also is used to measure the probability of an Option Contract Expiring “ITM” (In-The-Money). For Example, a Delta of 0.40 can be seen as a 40% chance to Expire ITM.
Gamma – An option’s Gamma is a measure of the rate of change of its delta. The gamma of an option is expressed as a percentage and reflects the change in the delta in response to a 1-point movement of the underlying stock price.
Measures the change in Delta from a 1$ movement in the underlying asset (stock, ETF, things like that). If the underlying moves an additional 1$ Then Delta would equal the Total of Delta + Gamma. After the First Dollar move, any additional moves in the same direction increases the value of Delta by the amount of Gamma.  
For Example, XYZ 100 12/31/20 Call for $1.00 and has a delta of .50 and a gamma of .05.
The price of XYZ moves 1 dollar upwards so the new price of the contract becomes 1.50.
The Price of XYZ moves 1 dollar upwards again so now we add both Delta AND Gamma to find the new value. (1.00...

The Greeks: What You Should Know Part 2
A lot of us know what the Greeks do individually but aren’t as certain on how they behave in relation to each other and the underlying asset. This write up will be done with the assumption you have read the previous post here:
Quick Example
Say John buys XYZ 100 1/15/21 Call (Buy-to-Open) for 1.00 and this contract has the following values:
Delta: 0.50 Gamma: 0.05 Theta: -0.02 Vega: 0.01
and the Current price of XYZ stock is $95.00.
This tells a lot but we will start with how Delta and Gamma work together:
(1) The Delta says that for every $1 move either up or down in price, will either decrease or increase the value of the option contract by 0.50 (e.g. $50). You will notice most option contracts are bought and measured for statistical purposes in the ranges of 0-0.20, .21-.40, .41-.60, .61-80, and .81-1.00.
(2) Then because Gamma is 0.05, for every change in Delta relative to a $1 movement in the underlying asset, The value of the option contract will increase by an additional 0.05 ($5) for every additional $1dollar change in the underlying assets price which would there create a correlated change in delta which is measured by gamma. So if the option contract for XYZ is 1.00 when the price of the underlying asset is $95 and then price moves up $1 dollar then the value of the contract becomes 1.50. (1.00 + 0.50) THEN, if the price moves an additional $1, Then the equation becomes, (1.50 + 0.50 + 0.05) = 2.05.
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